Melamine-barbiturate/cyanurate binary organogels possessing rigid azobenzene-tether moiety

Binary organogels were prepared from coaggregates of azobenzene-tethered melamine dimer and cyanurate/barbiturates. In the gels of hydrocarbon liquids, the coaggregates formed heavily entangled nanofibers, morphologies of which are dramatically different from the previously reported coaggregates based on flexible dodecamethylene-tethered melamine dimers. In the present systems, the rigidity of the azobenzene tether may induce regular packing of molecules. In addition, UV-vis and IR spectroscopic measurements provided unequivocal evidence for the contribution of the central amide groups and the azobenzene chromophores in the tether moiety upon forming well-defined nanofibers by hydrogen-bonding and face-to-face (H-type) pi-pi stacking interactions, respectively. As a result of tight molecular packing in the self-assembled nanofibers, the azobenzene moiety in the gel state showed remarkable resistance to trans --> cis isomerization upon irradiation with UV light.